Example embodiments of the inventive concept relate to a photodetector, and in particular, to a low-voltage high-gain high-speed germanium detector realized on a silicon substrate.
Recently, silicon photonics is actively being researched. Especially, a CMOS-compatible cost-effective high-performance germanium photo detector is being actively researched to realize an ultra-high-speed large capacity optical communication system and an image processing system, and speed and sensitivity of the photo detector are emerging as major issues. Further, there is an increasing interest in finding whether cost-effective high-performance silicon photonics-based germanium-on-silicon optical receivers can replace the conventional III-V compound semiconductor-based optical receiver.
A III-V compound semiconductor-based avalanche optical receiver, an expensive optical receiver, is widely used for a highly sensitive optical communication system. The III-V compound semiconductor-based avalanche optical receiver suffers from high fabrication cost and a high operation voltage for achieving high sensitivity. Recently, a research is being started to replace the III-V compound semiconductor avalanche optical receiver with a silicon photonics-based avalanche optical receiver. Compared with the III-V compound semiconductor-based optical device, the silicon-based optical device is cost-effective, and thus, it is expected to be commercialized. Further, the silicon-based optical device is superior in that it can be easily integrated with silicon electronic IC chips.
Nevertheless, to achieve high gain and high sensitivity, the silicon-based avalanche photodetector should be operated at a very high operation voltage (e.g., an avalanche voltage), and thus, it suffers from high power consumption. In this sense, there is a need to develop material and structure technology capable of realizing characteristics of low-voltage operation, high-gain, or high-speed.